1. Field of the Invention
The present invention pertains to a display device and more particularly relates to a liquid crystal display device manufacturing method for forming an oriented film by flexographic printing and allowing an increase of the yield of liquid crystal display devices, and a printing plate used in the flexographic printing.
2. Description of the Related Art
On a liquid crystal display panel used in a liquid crystal display device, a TFT substrate and a counter substrate are arranged. On the TFT substrate, pixels including pixel electrodes, thin film transistors (TFTs) and so forth are formed in a matrix. The counter substrate faces the TFT substrate and has color filters and so forth formed at locations corresponding to those of the pixel electrodes of the TFT substrate. A liquid crystal is nipped and held between the TFT substrate and the counter substrate. Then, an image is formed by controlling the transmittance of light through liquid crystal molecules per pixel.
In the liquid crystal display device, the liquid crystal molecule is initially oriented by the oriented films formed on the TFT substrate and the counter substrate, and the initially oriented state of the liquid crystal molecule is changed with an electric field which is formed between the pixel electrode and a counter electrode by applying an image signal to the pixel electrode, thereby controlling the quantity of light transmitted through the liquid crystal display panel. The direction of the initial orientation of the liquid crystal molecule is defined by performing a rubbing process or an optical orientation process on the oriented film.
In formation of the oriented film, an organic liquid material of a predetermined viscosity is applied onto the TFT substrate or the counter substrate, for example, by flexographic printing and thereafter a material of the oriented film is fired and imidized to form the oriented film. The flexographic printing of the oriented film is performed in the following manner. That is, the material of the oriented film is dripped onto a cylindrical anilox roll through an injection nozzle and then the material of the oriented film is uniformly applied onto the anilox roll using liquid spreading means (a doctor blade), and the uniformly applied material is transferred to a printing plate and then is printed from the printing plate onto the TFT substrate or the counter substrate.
In Japanese Patent Laid-Open No. Hei 6-305117, there is described a configuration that a variation in oriented film thickness is reduced by making the planar shape of a protruded part formed on an intersection of a lattice for retaining an oriented film liquid supplied from an anilox roll not circular but cruciform.
In Japanese Patent laid-Open No. 2004-78222, there is described a configuration that the density of protruded parts to be formed in a halftone dot or a lattice point of a printing plate is made denser on the periphery than at the center in order to prevent the thickness of the oriented film from increasing on the periphery.